When telephone cables were first developed, they were lead sheathed. Having made a splice between two cables, the splice was closed by means of a lead sleeve soldered to both cables. Re-access to the cable splice was obtained by breaking the soldered joints so that the lead sleeve could be slid back over one of the cables thereby revealing the splice. Re-closing was by sliding the sleeve back and re-soldering it to the cables.
With the advent of plastic sheathed cables, lead sheathed cables were phased out. However, the lead sleeving method of closing a cable splice was retained. To provide the necessary junction between the lead sleeve and the plastics sheathed cables, small tubular pieces of lead were attached to the cable ends. Tapes and epoxy resins have been used for this purpose. The lead sleeve was then simply soldered to the lead pieces.
The adaption of a first generation closure for use with second generation cable was obviously not entirely satisfactory. Failures occurred where the pieces of lead tubing were attached to the cables. Also, after a while, deterioration of the lead sleeve meant that it had to be replaced entirely. The only way this could be done was to split it lengthways, remove it and apply another sleeve which had previously been split lengthways. The new sleeve then had to have a totally air and watertight longitudinal seam formed in the wall thereof.
With the advent of synthetic plastics material which shrunk when heated, new possibilities were opened up. Various proposals were made, and indeed have been used commercially, all these methods relying on the ability of a sleeve of suitable synthetic plastic material to shrink onto a cable (or some other component of the closure) and form an air and watertight joint. The major drawback with prior proposals of this nature is that, to gain re-access to a previously closed splice, the sleeve must be destroyed. Normally this involves simply cutting the shrunk sleeve away and discarding it. Because the cable splice is permanent, it is not possible to slide a new sleeve on. After re-opening a splice the only way that it can be closed is to use a longitudinally split sleeve. Complex clamping and sealing arrangements are then required to close the longitudinal seam of the new sleeve.
In addition to the fact that destruction of major parts of the closure is necessary to gain access to the splice, subsequent re-closure requires a considerable degree of skill on the part of the workman. In one form a mastic is applied to the longitudinal seam and then clamps applied. After the closure has been re-opened, the previously used mastic must be cleaned away completely. If it is not cleaned away properly before the new mastic is applied, then the possibility exists that the longitudinal seam will not close properly.